Blood flow plays a significant role molding the developing heart, and the alterations in blood flow result in cardiovascular defects. A variety of experimental manipulations of its course, volume, or rate of flow have resulted in the production of a variety of cardiovascular anomalies. These alterations can affect development of the pumping heart, and the flow pattern of aortic arches well beyond the original site of altered flow. Evidence already exists that diverting flow from the left side of the developing heart to the right results in decrease in dorsal aortic flow and the active component of the atrioventricular blood flow (FASEB 10:A312, '96). Intracardiac flow patterns are altered in the right aortic arches, while left aortic arches flow is obliterated in the left atrial ligated chick embryo. Our specific hypothesis is that reducing flow through one side of the embryonic heart by diverting it to the other side would result in underdevelopment or hypoplasia of all structures on the affected side, with a corresponding overdevelopment or hyperplasia of the side into which this flow would be diverted. The results of this study, and from the previous work will demonstrate the importance of correlating functional and morphologic measurements in the study of cardiac development. A critical step in analyzing the functional relationships between developing cardiac form and function is the quantification of cardiac chamber and outflow tract dimensions. We propose to use MRM to measure the lumen volume of the ventricle and the cross sectional areas of the aortic arches in 1 normal stage 24 chick embryo and in 2 stage 24 embryos subjected to altered hemodynamics. With time permitting, we may also perform the same experiments on one normal stage 36 embryo and 2 stage 36 embryos subjected to altered hemodynamics.